A Little Known Legion in Northwestern Montana. 
203 
enough to pond back the waters and form the lake whose terraces I had 
seen. The southern extension of this lake was the steep-walled fiord¬ 
like valley of the upper St. Mary’s Lake. On the east the water was 
held in by the Milk River ridge; on the west by the mountains. How 
far north it extended would depend on the position of the hypothetical 
ice barrier. Lack of time prevented further investigation of this region. 
Ice records west of main range .— After crossing the continental divide 
the valleys on the western slope were found to give evidence of heavy 
glaciation. Planed surfaces and trains of bowlders were common but 
were confined to the valleys. Bowlders of undoubted glacial origin were 
found at an altitude of 7,250 feet. 
ORIGIN OF THE ICE-TONGUES OF THE EASTERN SLOPE OF THE ROCKY 
MOUNTAINS. 
In passing up along the eastern flank of the Rockies, as we came near 
enough to them to begin to encounter the moraines of the ice-streams 
spoken of in a previous paragraph, certain crystalline bowlders were oc¬ 
casionally observed. On examination they proved to be a rather fine¬ 
grained diorite. 
As we moved up the valley of the Cut-Bank these bowlders grew quite 
numerous. 
In the trip to the summit of Cut-Bank Pass it was confidently ex¬ 
pected that the outcrop of this diorite would be found. However, al¬ 
though the bowlders were to be seen all the way, the rocks in place 
seemed to be wholly of sedimentary origin and were very little if at all 
metamorphosed.* The failure to find the igneous rock was accounted 
for by supposing that it might now be hidden by debris from the cliffs 
above it. A second ascent was made up the Swift Current with no better 
results so far as finding the diorite was concerned. This valley is twenty 
miles from that of the Cut-Bank and there is no communication between 
them; but diorite bowlders occur in this valley also. 
The third ascent was by way of Belly River. As before stated, the bare 
walls of this valley afford no hiding place for beds of any prominence 
whatever. The exposure is peactically continuous for fifteen miles from 
the summit. No diorite or other eruptive or crystalline rock occurs in place 
in this valley. At the head of this river on the summit of Ahern Pass, at 
an altitude of 7,250 feet, bowlders of the diorite, some of them glaciated, 
were quite abundant. 
Some ten or twelve hundred feet below the summit, on the Pacific 
slope, a mile and a half from the pass, the diorite was found in place. 
The exposure is four miles in length. It occurs on both sides of the val¬ 
ley, which is fully a mile wide. 
* Diorite bowlders were seen however within 800 feet of the summit, at 7,000 feet eleva¬ 
tion. 
